The present invention relates to temperature controllers and particularly to a temperature controller for a hobbyist kiln.
Kiln temperature controllers for small kilns used by hobbyists have in the past been relatively unsophisticated and as a result, the kiln temperature frequently does not reach or alternatively exceeds the desired temperature. This adversely affects the outcome of the ceramic articles being fired both as to the color of the articles as well as the physical properties of the ceramic material itself. Kiln temperature controllers for the hobbyist have involved, for example, mechanical controllers which use a meltable material positioned between spring loaded contacts to actuate the kiln heater at predetermined temperatures. Frequently these controllers do not operate at all or do not operate at the desired temperature to control the kiln temperature.
In other temperature controllers where thermocouples are employed to measure the temperature as well as turn off the kiln at a predetermined desired temperature; problems have been encountered with the ambient temperature variations which the temperature controller is subjected to. This results since the measuring thermocouple made of dissimilar metal wires when coupled to a circuit board or connector forms a second thermocouple junction in the controller which is remote from the temperature measuring thermocouple in the kiln and is subjected to varying ambient temperatures near the kiln. As the ambient temperature changes typically with the kiln temperature, the measurement thermocouple output becomes relatively inaccurate due to the added signal from the second junction. Temperature responsive resistors have been employed in an effort to compensate for this but without any significant success. Since the ambient temperature variations are unpredictable, due in part to the positioning of the kiln temperature controller at an individual installation and other variable factors including the location of the kiln with respect to the surrounding environment; no known adequate solution has yet been provided for correcting this problem.
Also it has long been recognized that the optimum temperature rise in the kiln for firing a ceramic article is approximately 270.degree. F. per hour. Efforts to provide a kiln temperature controller to effect such temperature rise has involved the use of manually operated heater switches or bi-metallic infinite temperature controlling switches. Such systems either require nearly continuous operator attention or otherwise do not adequately control the temperature use time of the kiln.